vrend: fix a stack overflow in set framebuffer state

Add the sanity check of the 'nr_cbufs' to avoid stack
overflow.

Signed-off-by: Li Qiang <liq3ea@gmail.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

src/vrend_decode.c

@@ -136,6 +136,10 @@ static int vrend_decode_set_framebuffer_state(struct vrend_decode_ctx *ctx, int
 
    if (length != (2 + nr_cbufs))
       return EINVAL;
+
+   if (nr_cbufs > 8)
+      return EINVAL;
+
    for (i = 0; i < nr_cbufs; i++)
       surf_handle[i] = get_buf_entry(ctx, VIRGL_SET_FRAMEBUFFER_STATE_CBUF_HANDLE(i));
    vrend_set_framebuffer_state(ctx->grctx, nr_cbufs, surf_handle, zsurf_handle);